The present invention relates to an improved process for producing alkylaromatics, for example, ethylbenzene, cumene and sec-butylbenzene.
Of the alkylaromatic compounds advantageously produced by the present improved process, ethylbenzene and cumene, for example, are valuable commodity chemicals which are used industrially for the production of styrene monomer and coproduction of phenol and acetone respectively. In fact, a common route for the production of phenol comprises a process which involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide, and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. Ethylbenzene may be produced by a number of different chemical processes. One process which has achieved a significant degree of commercial success is the vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic ZSM-5 zeolite catalyst. Examples of such ethylbenzene production processes are described in U.S. Pat. Nos. 3,751,504 (Keown), 4,547,605 (Kresge) and 4,016,218 (Haag).
Another process which has achieved significant commercial success is the liquid phase process for producing ethylbenzene from benzene and ethylene since it operates at a lower temperature than the vapor phase counterpart and hence tends to result in lower yields of by-products. For example, U.S. Pat. No. 4,891,458 (Innes) describes the liquid phase synthesis of ethylbenzene with zeolite beta, whereas U.S. Pat. No. 5,334,795 (Chu) describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene. The latter patent teaches use of catalyst comprising MCM-22 crystalline material and binder in the ratio of crystal/binder of from about 1/99 to about 90/10.
Cumene has for many years been produced commercially by the liquid phase alkylation of benzene with propylene over a Friedel-Craft catalyst, particularly solid phosphoric acid or aluminum chloride. More recently, however, zeolite-based catalyst systems have been found to be more active and selective for propylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606 (Kushnerick) describes the use of MCM-22 in the liquid phase alkylation of benzene with propylene.
Other publications show use of catalysts comprising crystalline zeolites and binders for conversion of feedstock comprising an alkylatable aromatic compound and an alkylating agent to alkylaromatic conversion product under at least partial liquid phase conversion conditions. These include U.S. 2005/0197517A1 (Cheng) showing use of a catalyst crystal/binder ratio of 65/35 and 100/0; U.S. 2002/0137977A1 (Hendriksen) showing use of a catalyst crystal/binder ratio of 100/0 while noting the perceived negative effect of binders on selectivity; U.S. 2004/0138051A1 (Shan) showing use of a catalyst comprising a microporous zeolite embedded in a mesoporous support, where the zeolite/support ratio is from less than 1/99 to more than 99/1, preferably from 3/97 to 90/10; WO 2006/002805 (Span) teaching use of a catalyst crystal/binder ratio of 20/80 to 95/5, exemplifying 55/45; U.S. Pat. No. 6,376,730 (Jan) showing use of layered catalyst crystal/binder of 70/30 and 83/17; EP 0847802B1 showing use of a catalyst crystal/binder ratio of from 50/50 to 95/5, preferably from 70/30 to 90/10; and U.S. Pat. No. 5,600,050 (Huang) showing use of catalyst comprising 30 to 70 wt. % H-Beta zeolite, 0.5 to 10 wt. % halogen, and the remainder alumina binder.
Existing alkylation processes for producing alkylaromatic compounds, for example, ethylbenzene and cumene, inherently produce polyalkylated species as well as the desired monoalkyated product. It is therefore normal to transalkylate the polyalkylated species with additional aromatic feed, for example benzene, to produce additional monoalkylated product, for example ethylbenzene or cumene, either by recycling the polyalkylated species to the alkylation reactor or, more frequently, by feeding the polyalkylated species to a separate transalkylation reactor. Examples of catalysts which have been used in the alkylation of aromatic species, such as alkylation of benzene with ethylene or propylene, and in the transalkylation of polyalkylated species, such as polyethylbenzenes and polyisopropylbenzenes, are listed in U.S. Pat. No. 5,557,024 (Cheng) and include MCM-49, MCM-22, PSH-3, SSZ-25, zeolite X, zeolite Y, zeolite Beta, acid dealuminized mordenite and TEA-mordenite. Transalkylation over a small crystal (<0.5 micron) form of TEA-mordenite is also disclosed in U.S. Pat. No. 6,984,764.
Where the alkylation step is performed in the liquid phase, it is also desirable to conduct the transalkylation step under liquid phase conditions. However, by operating at relatively low temperatures, liquid phase processes impose increased requirements on the catalyst, particularly in the transalkylation step where the bulky polyalkylated species must be converted to additional monoalkylated product without producing unwanted by-products. This has proven to be a significant problem in the case of cumene production where existing catalysts have either lacked the desired activity or have resulted in the production of significant quantities of by-products such as ethylbenzene and n-propylbenzene.
Although it is suggested in the art that catalysts for conversion of feedstock comprising an alkylatable aromatic compound and an alkylating agent to alkylaromatic conversion product under at least partial liquid phase conversion conditions are composed of a porous crystalline aluminosilicate and binder in the ratio of crystal/binder of from 1/99, e.g., 5/95, to 100/0, current commercial catalysts, i.e., those found to be commercially useful, for this process are composed of a porous crystalline aluminosilicate and binder in the ratio of crystal/binder of either 65/35 or 80/20. Finding a commercially acceptable catalyst for such processes conducted under at lease partial liquid phase conversion conditions which increases monoselectivity, i.e., lower di- or polyalkyl product make, would allow capacity expansion in existing plants and lower capital expense for grassroots plants as a result of lower aromatic compound/alkylating agent ratios. According to the present invention, it has now unexpectedly been found that a liquid phase or partial liquid phase alkylation process for producing alkylaromatics conducted in the presence of a specific catalyst comprising a porous crystalline material, e.g., a crystalline aluminosilicate, (“crystal”) and binder in the ratio of crystal/binder of from about 20/80 to about 60/40, yields a unique combination of activity and, importantly, monoselectivity. This is especially the case when the process involves at least partial liquid phase alkylation for manufacture of ethylbenzene or cumene. This obviates or lessens the demand in many instances for the difficult transalkylation reaction for conversion of unwanted bulky polyalkylated species in such a process.